The present invention relates to filters capable of removing various contaminants, including pathogens, from liquids by filtration. In particular, it relates to filters that comprise activated carbon fibers for removing a broad spectrum of contaminants, including viruses, from liquids. Additionally, it relates to a method of removing contaminants from liquids.
Water may contain many different kinds of contaminants including, for example, particulates, harmful chemicals, and microbiological organisms, such as bacteria, parasites, protozoa and viruses. In a variety of circumstances, these contaminants must be removed before the water can be used. For example, in many medical applications and in the manufacture of certain electronic components, extremely pure water is required. As a more common example, any harmful contaminants must be removed from water before it is potable, i.e., fit to consume. Despite modern water purification means, the general population is at risk, and in particular infants and persons with compromised immune systems are at considerable risk.
In the U.S. and other developed countries, municipally treated water typically includes one or more of the following impurities: suspended solids, bacteria, parasites, viruses, organic matter, heavy metals, and chlorine. Breakdown and other problems with water treatment systems sometimes lead to incomplete removal of potential pathogens. For example, cryptosporidiosis, a type of waterborne microbiological contamination, was brought to national attention in April of 1993 when the water supply of the city of Milwaukee, Wis. became contaminated with cryptosporidium cysts resulting in 400,000 cases of the disease and over 100 related deaths.
In other countries there are deadly consequences associated with exposure to contaminated water, as some of them have increasing population densities, increasingly scarce water resources, and no water treatment utilities. It is common for sources of drinking water to be in close proximity to human and animal waste, such that microbiological contamination is a major health concern. As a result of waterborne microbiological contamination, an estimated six million people die each year, half of which are children under 5 years of age.
In the U.S., the National Sanitation Foundation (NSF), based on Environmental Protection Agency (EPA) studies, introduced standards that must be met for drinking water. The purpose of these standards is to establish minimum requirements regarding the performance of drinking water treatment systems that are designed to reduce specific health related contaminants in public or private water supplies. Established in 1997, Standard 53 requires that the effluent from a water supply source exhibit 99.9% removal of parasites against a challenge. Established in 1991, Standard 55 requires that the effluent from a water supply source exhibit 99.99% removal of viruses and 99.9999% removal of bacteria against a challenge. One microorganism for each class of pathogen is used to demonstrate that the filter system is adequately treating for the respective pathogens. As a representative microorganism for parasites/protozoa, cryptosporidium is used. Because of the prevalence of E. coli (bacterium) in water supplies, and the risks associated with its consumption, this micro-organism is typically used as the bacterium. Also, MS-2 bacteriophage is typically used as the representative microorganism for virus removal because its size and shape (i.e., 25 nm and spherical) make it a particularly difficult microorganism to be removed from liquids, relative to other viruses. Thus, a filter""s ability to remove MS-2 bacteriophage demonstrates its ability to remove other viruses
Therefore there is a need for a filter capable of removing a broad spectrum of contaminants. This filter would comprise a single, small, lightweight, self-contained system rather than a complex multi-component and/or multistage system to remove the various contaminants. Such a filter would not only be more reliable than a complex system, but it would also be far more portable and economical. Thus, it could be utilized as a simple device on faucets in domestic settings where well water or water from a municipal source is used. In another application, such a device could be utilized in lesser developed regions of the world on a faucet or container for storing drinking water, where communal water sources are shared, but little is done to treat the water for contamination. A small, inexpensive, easy-to-use, water filter would be of great humanitarian and economic value. In certain applications, the filter should present a low resistance to the flow of water so that in locations where electricity necessary to drive a pump may be unavailable, the filter may simply be connected between upper and lower containers of water, or between the holding container and a drinking receptacle. In certain embodiments, the filter should also have sufficient structural integrity to withstand significant pressures if, for example, a source of pressure is available to drive the liquid through the filtering apparatus (e.g. mechanical pump, faucet pumped water, etc.).
Despite centuries of a well-recognized need and many development efforts, activated carbon in its various forms has never been shown to reliably remove pathogens from water or enjoyed wide-spread commercial use for pathogen removal per se. Many attempts have been made over the years to apply activated carbon to pathogen removal without notable success. In the United States, the patent literature reflects that improved activated carbon materials and water treatment structures have been sought for water purification since at least the 1800xe2x80x2s. For example, U.S. Pat. No. 29,560 teaches that an adsorptive carbon can be made by combining peat, cut out of the bog, with chalk in water to make a paste, followed by molding and firing. U.S. Pat. No. 286,370 teaches that artificial bone black blocks made from a slurry of finely powdered charred bones and magnesia can be used to good effect in water filters.
The prior art teaches away from using activated carbon alone, by teaching that a supplemental means must be used for pathogen removal, such as the use of biocides, pasteurization (heating), electricity, distillation or high-energy radiation such as UV or X-rays. Additionally, the U.S. EPA has taught against the use of activated carbon alone for pathogen removal, stating that xe2x80x9cactivated carbon [even] with silver does not eliminate all bacteria in water and cannot remove protozoa and viruses.xe2x80x9d (See 59 Federal Register 223, Nov. 21, 1994.) As an example of the use of separate pathogen removal means, U.S. Pat. No. 4,828,698 (Jewell et al., issued May 9, 1989) teaches the use of a microporous membrane having pore sizes from 0.02 xcexcm to 0.5 xcexcm for microbiological control. U.S. Pat. No. 4,576,929 (Shimazaki et al., issued Mar. 18, 1986); U.S. Pat. No. 5,705,269 (Leiberman, issued Jan. 6, 1998); and U.S. Pat. No. 5,607,595 (Hiasa et al., issued Mar. 4, 1997) teach the use of silver, organic pesticides, and periodic heating to supplement activated carbon use. U.S. Pat. No. 3,770,625 (Wallis et al., issued Nov. 6, 1973) teaches that viruses can be removed from a liquid using activated carbon forms (granular, powdered or pelleted) treated with a sodium containing hydrolyzing composition, such as sodium hydroxide, after an acid wash. The ""625 patent further teaches that the method did not provide stand-alone treatment stating xe2x80x9cit is frequently desirable to have filtration downstream of the activated charcoal to remove any sluffed-off adsorbing medium.xe2x80x9d U.S. Pat. No. 5,762,797 (Patrick et al., issued Jun. 9, 1998) discloses the use of a separate nonwoven, which is treated with an antibacterial material, to effect treatment of the bacteria. German Patent Publication No. 3,020,615 (Beauman et al., published Dec. 11, 1980) discloses the addition of silver-containing compounds to effect antibacterial activity. More recently, activated carbon fibers have been employed in water purification/filtration devices. See, e.g., U.S. Pat. No. 4,576,929 (Shimazaki, issued Mar. 18, 1986), U.S. Pat. No. 5,705,269 (Pimenov et al., issued Jan. 6, 1998), and European Patent No. EP 366,539B 1 (Kaneko, published Mar. 25, 1998). While these and other prior art references have previously utilized activated carbon, including activated carbon fibers, in water filters, it is evident that the activated carbon is being employed to remove organic matter. Thus, to the extent that certain prior art references disclose the use of activated carbon to treat a water source with respect to pathogen removal, including viruses, such approaches require the use of additional treatment steps or they require a relatively complex assembly of components.
In view of the foregoing, it has now been surprisingly discovered that a filter comprising activated carbon fibers alone can reliably remove a wide range of microorganisms from water, including very small microorganisms such as MS-2 bacteriophage to much larger pathogens such as E. coli bacteria. Accordingly, an object of the present invention is to provide an improved filter for removing contaminants from a water source. A specific object includes providing a water filter which removes a broad spectrum of contaminants, including pathogens and in particular viruses from the water source. The removal of such pathogens using the present filter is at a level not previously demonstrated by the prior art. Such a filter will preferably present a low resistance to the flow of liquid through the apparatus, and will remove the contaminants from a substantial volume of water before becoming saturated. In certain embodiments, the filter will also preferably be relatively portable.
A process for forming an activated carbon fiber filter for removing viruses from liquids is provided. The process includes selecting a plurality of activated carbon fibers, placing the activated carbon fibers in a hollow form open at least one end, and applying a predetermined compressive force to the fibers along the axis through the hollow form parallel to the direction in which the liquid will pass until the fibers are densely and uniformly packed within the form.